Cellular communication devices use network radio access technologies to communicate wirelessly with geographically distributed cellular base stations. Long-Term Evolution (LTE) is an example of a widely implemented radio access technology that is used in 4th Generation (4G) communication systems. New Radio (NR) is a newer radio access technology that is used in 5th Generation (5G) communication systems. Standards for LTE and NR radio access technologies have been developed by the Third-Generation Partnership Project (3GPP) for use by wireless communication carriers. There are several proposed configurations for 4G/5G dual connectivity, and communications between network components may be implemented in various ways.
A communication protocol defined by the 3GPP, referred to as EN-DC (E-UTRAN/New Radio-Dual Connectivity) enables the simultaneous use of LTE and NR radio access technologies for communications between a mobile device and a cellular communications network. EN-DC may also be referred to as LTE/NR dual connectivity. EN-DC is described by 3GPP Technical Specification (TS) 37.340 and others.
EN-DC can be implemented in conjunction with a 4G core network, with the support of 5G base stations, in a configuration known as Non-Standalone Architecture (NSA). In this configuration, a 4G LTE base station (referred to as a Master eNodeB or MeNB) is associated with a 5G NR base station (referred to as a Secondary gNodeB or SgNB). In an NSA system, both the LTE base station and the NR base station exchange data via a 4G core network. However, control communications are between the 4G core network and the LTE base station, and the LTE base station is configured to communicate with and to control the NR base station. In an NSA system, a mobile device initially connects to an LTE base station.